Proj Overview

Project Overview


Construction of Foothills Bridge No. 2, in Blount County, Tenn., was instrumental to completing a final piece of the 75 mi (120 km) long Foothills Parkway. The parkway was authorized by Congress in 1944 to provide grand vistas of the Great Smoky Mountains National Park. It is administered by the National Park Service, which partners with the Federal Highway Administration to develop infrastructure within national parklands.

This exceptionally rugged 1.6 mi (2.6 km) stretch of parkway traverses steep mountainsides and presented serious logistical challenges.

From the outset, everyone on the team recognized that the project faced serious challenges and would require innovative design and planning to pull it off, says Rick Merritt, of Ross Prestressed Concrete, the precaster on the project. "Site access was only available from the beginning of the bridge and via the especially steep and rugged terrain along the entire length of the alignment."

To minimize site disruption while managing costs and meeting the aesthetic requirements of the owner, the designers chose high-performance precast concrete. "Precast concrete allowed the owner to mimic the mountain terrain geometrically and, by coloring the concrete to match the native rock, gently blend into the natural landscape very nicely," Merritt says.

It also helped address the uneven mountain terrain. "The mountain landscape dictated a bridge geometry with an undulating footprint and up to 8% reversing cross slopes on an 8% grade," Merritt says. "So every segment we produced was unique in its geometry."

To address construction challenges along the steep terrain, the designers originally planned to do a progressive segment erection, but that plan was dismissed because the strictly linear approach would not meet the project schedule, Merritt says. "A new approach was required that allowed various aspects of precast concrete construction to be performed concurrently."

Precast Solution

The new construction methodology incorporated a temporary work trestle that provided access along the entire bridge alignment and could be reconfigured as work shifted from foundation and precast concrete segmental piers to superstructure segment erection. A specialized segment walker placed segments in balanced cantilevers, significantly increasing erection speed over one-direction progressive placement methods.

"The segment walker moves by sliding pairs of support feet, with one of the sliding feet in each pair always tied to the work trestle," Merritt says. "This continual fixity greatly improved the safety of construction on the steep bridge grade."

The designer's innovative design-build approach successfully achieved the goals of all project stakeholders. Environmental impacts were also limited to selective tree toppings and minimized disturbance of fragile topsoil, which was critical on the protected forest land.

"This project was unique both to our company and this area of the country," Merritt says. "High-performance concrete was employed, resulting in a structure with a 75- to 100-year expected life span, ensuring many future generations will enjoy the magnificent beauty of the Great Smoky Mountains from the vantage point of Bridge No. 2."

 

Awards
2014 Design AwardsDesign Award Transportation: Best Bridge with a Main Span over 150 Feet
Project Team

Owner

National Park Service 

Owner's Engineering Representative

Eastern Federal Lands Highway Division 

Engineer of Record

Corven Engineering, Inc. 

Precaster

Ross Prestressed Concrete, Inc

Precast Concrete Specialty Engineer

Corven Engineering, Inc 

Contractor

Bell and Associates Construction LP 

Photo Credit

Bell and Associates Construction and Corven Engineering Inc.

Key Project Attributes

  • Precast concrete allowed the owner to mimic the mountain terrain geometrically and to color the concrete to match the natural landscape
  • Precast concrete minimized site disruption while managing costs and meeting aesthetic requirements
  • The resiliency of precast concrete results with a 75- to 100-year expected life span

Project/Precast Scope

  • Project Cost: $25 million
  • Bridge Length: 790 ft (241 m)